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Since the signals in solid state NMR are often very broad, the spins dephase quickly, allowing only a short time for observation.
The spectrometers [[dead time]] can therefore become a significant problem. To overcome this, a second pulse phased 90° relative to the original excitation, can be used to trigger rephasing of the spins. The time between these two pulses should (in theory) be equal to the [[dead time]], so that the spins are rephased once aquesition begins.

Usually <math>\tau</math> is chosen to be bigger than ''DT'', to make sure that the signal maximum of the echo is observed. The FID is then left shifted until the signal maximum is at the beginning.

==Spin Echo==

The spin-echo (or hahn-echo) pulse sequence is useful for lines broadened by chemical shift anisotropy or heteronuclear dipole-dipole couplings.

<pulse>
anchors:   @a        @b       @c    @d 
disp:     2@a      6@b     6@c  8@d   
time:  rlx @a   t1   @b   dt  @c aq @d 
rf H:    90@a=p1  180@b=p2 acq@c-----d

delay rlx: hide=true
delay t1: label=\tau
delay dt: label=\mathrm{DT}

acq: type=fid

rfchan H: label=^1H

pulse p1: phase=phi1
pulse p2: phase=phi2

phase phi1: label=\mathrm{+X}
phase phi2: label=\mathrm{+Y}
</pulse>

==Solid Echo==

The solid-echo (or quadropole-echo) pulse sequence is used for lines broadened by quadropole coupling or homonuclear dipole-dipole coupling.

<pulse>
anchors:   @a        @b       @c    @d 
disp:     2@a      6@b     6@c  8@d   
time:  rlx @a   t1   @b   dt  @c aq @d 
rf H:    90@a=p1   90@b=p2 acq@c-----d

delay rlx: hide=true
delay t1: label=\tau
delay dt: label=\mathrm{DT}

acq: type=fid

rfchan H: label=^1H

pulse p1: phase=phi1
pulse p2: phase=phi2

phase phi1: label=\mathrm{+X}
phase phi2: label=\mathrm{+Y}
</pulse>
[[Category:NMR experiment]]
[[Category:NMR concept]]
[[Category:Add citations]]

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